1. Field of the Invention
The invention relates to a propulsive device for accelerating flow of a fluid passing through the device, particularly for use as a fluid pump for pumping fluids, for propelling or separating solids carried in fluids, or for propelling the device through a fluid.
2. Prior Art
The term "fluid" herein refers to liquids, gases or a mixture of both. Many types of fluid propulsive devices are known, some of which use a powered rotating member which rotates within the fluid, such as a common propeller as used in marine vessels or aircraft, or an impeller as used in centrifugal or vane pumps. Some of these common pumps are relatively inefficient and when used to pump a fluid carrying relatively fragile solids, the rotating member can damage the solids. Many of such pumps could not be used for separating fine solids carried in fluids.
Some of the limitations above are overcome by using jet pumps, such as injectors, ejectors, eductors, etc. Such pumps use a common fluid pump as a primary pump to produce a central jet of working fluid within a duct carrying a main fluid, which jet accelerates flow of the main fluid through the duct. In many jet pumps, power consumed by the primary pump in pumping the working fluid far exceeds the power than would have been required for pumping the main fluid using only a common rotary fluid pump. Such jet pumps are thus generally relatively inefficient and consequently are usually used only in applications where the normal rotary pump is not practical, for instance when transporting fragile solids carried in the main fluid.
Some authorities feel that the relative inefficiency of the common jet pump results from two major factors. Firstly, there is a relatively large velocity difference between the working and main fluids during mixing, which produces turbulence resulting in excessive energy losses. Secondly, a viscous boundary layer formed adjacent the duct side wall reduces efficiency of the device by reducing flow rate.